Method of and apparatus for precision coring in the casting of metallic articles



G. R. SANDENBURGH ETAL 2 July 21 METHOD OF AND APPARATUS FOR PRECISIONCORING IN THE CASTING OF METALLIC ARTICLES Filed July ll, 1955 METHOD FAND APPARATUS FOR PRECISIQN CORING IN THE CASTING 0F METALLIC AR- TICLESGeorge R. Sandenburgh, Evanston, and Marshall D. King, Wood Dale, Ill.;said Sandenburgh assiguor to H1lls McCanna Company, Chicago, lll., acorporation of Illinois Application July 11, 1955, Serial No. 521,236

3 Claims. (Cl. 22-131) The `invention relates to a method of formingcored passageways in castings of aluminum or magnesium alloys and hasreference in particular to the formation of cored passageways of complexand unusual shape and wherein a high degree of accuracy is obtained inthe castings as to the internal diameter, conguration and location ofthe resulting passageways.

The invention has for its principal object to provide a method of coringintricate and complex passageways in aluminum or magnesium alloycastings which is characterized by a high degree of dimensionalaccuracy, wherein thermal expansion due to the heating of the core priorto pouring the casting or due Ato the high temperature of the moltenmetal during the pouring operation need not be considered in iiguringthe core dimensions since the passageways cored by the present methodwill not deviate from the specified dimensions on the drawings of thearticle to be cast by more than permitted foundry tolerances, andwherein actual drawing dimensions can therefore be used exclusively indetermining the size, conguration and location for the core material.

There are certain problems inherent in the use of sand cores which limittheir use in the production of passageways of small diameter in castingsof light alloys such as aluminum or magnesium. When molten metal isintroduced into the casting cavity so as to contact with sand cores,gases are formed by Volatilization of the chemical inhibitors and corebinders. These gases can not be allowed to bubble through the moltenmetal, on the contrary, the `gases must be permitted to escape throughthe core interior and out to the atmosphere. Sand cores have naturalpermeability but in long, thin or intricate cores it is necessary toform an interior cavity `called a vent for the escape of these gases.The interior cavity in the core naturally decreases it strength and thusincreases the chances of the core breaking. In thin, intricate coreshaving unsupported lengths of more than a few inches, it is commonpractice to insert a steel wire for support. However, these wiresintroduce inaccuracies into the core during casing, due to thedifferential in thermal expansion between sand and the steel wires. Thesame is apt to cause warpage of the core, especially in intricateshapes.

Because of the above difficulties in the use of sand cores for intricateand small interior passageways in cast metal articles, -it has becomestandard practice to cast solid sections and drill or otherwise machinethe desired passageways in the castings. Drilling is not entirelysatisfactory since it has limitations and in addition the procedure isVery costly.

The above difficulties have been successfully solved by the techniquesof the present invention which contemplate the use of preformed hollowglass tubing as core material. In particular the invention contemplatesthe use of. borosilicate glass tubing for producing smooth-surfacedpassageways in castings of aluminum or magnesium alloys. Borosilicateglass, commercially known as Pyrex vnited States Patent 0 2,895,191Patented July 21, 1959 ICC glass, has a number of characteristicsparticularly adapting it for use as coring material in the production ofpassageways -in light alloy castings. In the first place, borosilicateglass is a commercially available product, relatively inexpensive, andwhich can be purchased in a variety of shapes and sizes. Secondly, theaccurate retention of the core dimensons when borosilicate glass is usedis the result of its high resistance to thermal shock and poor heattransfer characteristics of the glass, plus the fact that the glass isput in compression from instantaneous solidiication, and contraction ofthe immediately formed metal layer surrounding and in contact with `theglass wall exterior, and also combined with the thermal gradient andresultant stress within the wall of the tube tending to causecompression.

During the time cycle of the pouring and solidication of the metalaround the tube, the glass will soften and reach a plastic state fromheat, which, plastic state then temporarily accommodates stress andalignment requirements with the hot solidifying metal mass, so that,upon total solidication, the glass core will still maintain itself in asolid, physical, unbroken state to achieve its inherent functions offorming a passageway and still main- Itain its precision of placement.

In View of the foregoing, another object of the invention resides in theuse of borosilicate glass as coring material in the formation ofintricate passageways in aluminum or magnesium castings. Said glass iscapable of withstanding the pouring temperatures for alloys of aluminumand magnesium, and thus cores formed of said material will retain theirpredetermined shape during the pouring operation. Also the said glass ascoring material is highly satisfactory in retaining its position,alignment and dimensional accuracy during pouring, notwithstanding somesoftening of the glass and movement thereof during cooling and shrinkingof the casting.

Another object of the invention is to produce intricate passageways inaluminum and magnesium castings using borosilicate glass as the coringmaterial, wherein lit is accordingly possible to dimension the cores byusing the actual dimensions `therefor appearing on the drawings of thearticle -to be cast, and lwherein the same shrinkage allowances can beemployed for both the pattern and the core.

With these and various other objects in view, the invention may consistof certain novel features of construction and operaiton as will be morefully described and particularly pointed out in the specification,drawings and claims appended thereto.

In Ithe drawings which illustrate an embodiment of the invention andwherein like reference characters are used to designate like parts-Figure l is an elevational View of the completed casting having internalpassageways formed therein as indicated by dotted lines;

Figure 2 is a sectional view taken along line 2--2 of Figure l to moreparticularly illustrate the size, coniguration and location of the coredpassageways in the completed casting;

Figure 3 is an end elevational view of the pattern required forproducing the casting as shown in Figure l;

Figure 4 is a top plan view of the pattern as shown in Figure 3;

Figure 5 is an end elevational View of the `borosilicate glass core usedin the production of the intricate passageways;

Figure 6 is a top plan View of the glass core shown in Figure 5;

Figure 7 is a top plan view of the mold used in casting the articleshown in Figure l; and

Figure 8 is a transverse sectional view taken along line 8-8 of Figure7.

Referring to the drawings and particularly Fgures 1 and 2, the castingselected for illustrating the invention is generally indicated'by thenumeral 10, the same being formed of` a light metal such as a magnesium.alloy. The' casting 10 is substantially rectangular in shape and thesame is characterized by having a plurality of passageways formedtherein of an intricate and complex configuration. The passagewaysterminate in the four outlets such as 11, 12, 13 and 14, in the topsurface 15 of the casting, and said outlets communicate with theinterior connecting passageway generally indicated by numeral 16, andincluding the sloping passageways 17 and 18 and a connecting passageway19.

Figures -3 and 4 disclose a pattern 20 designed for use in producing thesaid casting 10. The pattern 2t) essentially consists of a body portion2.1 having the same rectangular shape as that of the casting. To providethe. core prints in the mold, the top surface 22 of the pattern isprovided with the tubular projections identified by numerals 23, 24, 25and 26 and which correspond in shape and in location to the outletpassageways 11, 12, 13 and 14.

Figures and 6 disclose the core which is located within the'mold cavityfor producing the passageways. In accordance with the invention the coreis formed of borosilicate glass, and said core, generally indicated bynumeral 30, has the shape and configuration desired of the passagewaysfor the completed casting. Accordingly, four projections such as 31, 32,33 and 34 are provided which correspond in shape and in position to theoutlet passageways 11 to 14 inclusive. As best shown in Figure 6, thesaid four glass projections are joined by a body portion 35 whichincludes the sloping portions 36 and 37 and the connecting portion 38.The core 3) consists of a borosilicate glass tube. In any event, it willbe understood that the core is of the appropriate size and shape and hasthe proper configuration for producing the desired passageways in thecompleted casting. The glass core can be formed by heat or byconventional glass blowing, or molding operations, and for moreintricate and complex passageways Various sections of said coringmaterial, or an assembly of blown glass sections, can be set in the moldcavity for subsequent pouring operations.

Due to the beneficial combination existing between the borosilicateglass cores and the casting metal of either aluminum or magnesium alloythe dimensions for both the pattern and the core can be taken directlyIfrom the drawings of the part to be cast. The pattern dimensions as wellas the core dimensions would, howver, be expanded by a factor tocompensate for the thermal. contraction which occurs between thesolidification temperature of the casting material and the roomtemperature thereof. However, it is not necessary to consider thethermal expansion due to heating of the core prior to pouring thecasting, or due to the temperature ofthe molten metal employed in thepouring operation since the passageways produced by the borosilicatematerial will not deviate from. the drawing dimensions by more thanspecified foundry tolerances. As regards the core 30, as shown inFigures 5 and 6, the same was produced using the actual dimensions asthey appeared on a drawing of the part. Of course, the dimensions wereexpanded by the same shrinkage allowances as were used in theconstruction of the pattern. The core was then checked dimensionallyprior to pouring of the casting and the resulting casting wassubsequently sectioned and the passageway laid out. A comparison of thetwo sets of dimensions disclosed that the cored passageway `was withinthirty-thousandths of the core dimensions. Whereas, aluminum andmagnesium alloys constitute the preferred metals for the present glasscoring technique, nevertheless the same is not necessarily limited tosuch alloys but can also be used in connection with other alloys havingmelting points below the softening point of the glass core whereby thecore will not become distorted during the casting operation.

In Figures 7 and 8 the numeral 40 indicates a standard flask which isfilled with sand 41. The preformed glass core assembly 3) is properlyset within the mold cavity 42 with the glass ends or projections such as31 to 34 inclusive being rmly held in proper position in the core prints43 to 46, respectively. The mold cavity 42 is provided with a pluralityof pouring gates and risers 47 and which are suitably connected by theruimer 48.

In practice the molten alloy is poured into the prepared mold until themold cavity is lled and whereby the molten metal completely surroundsthe core material. The metal solidiiies in place and the glass core,which now forms the liner, or is actually the hole former in thesolidied metal, remains intact without fracture or appreciabledistortion or melting of the glass. The casting 10 is next removed fromthe mold and the projections, due to the pouring gates and risers, whichare attached thereto, are removed and the rough casting is now ready forremoval of the core material.

For this operation the casting `and core assembly may be submerged in areagent selected for corroding the glass but which will not have anyappreciable corrosion effect on the metal of the casting. Hydrotluoricacid or aqueous solutions of iluophosphoric acid with or withoutinhibitors such as arsenic oxide may be used. The reagent is permittedto selectively corrode the glass so that after a period of time thecoring material will be completely removed, leaving precise andaccurately formed passageways in the metal of the casting. When glasstubing is employed as the coring material, the corroding reagent may becaused to ow through the tubing and thus it is not necessary for theentire casting to be submerged in the reagent. When using the glasscoring techniques as described for producing passageways in castings ofmagnesium and aluminum the gates and risers should be so located astoprevent any possibility of partial melting and/ or distortion of theglass core assemblies. In general, the gates and the risers should belocated at a distance as far as possible from the glass cores.

Itis thus possible with the method of the present invention to useactual drawing dimensions exclusively in determining the configurationsof the core and its location within the mold, and it is only necessarythat they be expanded by the same shrinkage allowances as used intheconstruction of the pattern. In addition to light alloy castings ofaluminum and magnesium, other metals having pouring temperatures as highas l700 Fahr. may be cast in accordance with the invention. Of course,in such cases it is necessary to select glass composition for the coringmaterial such as will withstand the pouring temperature of the metalbeing cast. Also the glass coring material should retain itspredetermined design shape and it should be possible to corrode thecoring material by a selective reagent without appreciable corrosion ofthe metal of the casting. Borosilicate glass having a typicalcomposition such as SO2-80%; B2O3-l4%; Na2O-4%; Al2O3-2% is preferred inthe glass cores since in addition to the above properties it ischaracterized by a relatively low coefficient of thermal expansion and ahigh resistance tothermal shock. Accordingly, the precisionl which isobtained in the core position and alignment and the high degree ofdimensional accuracy, as regards the cored passageways, is directly dueto these characteristics' in the glass coring material as they areexhibited when in combination with light weight metals such as alloys ofaluminum and magnesium.

The invention is not to be limited to or by details of construction ofthe particular embodiment thereof illustrated by the drawings, asvarious other forms of the device will of course be apparent to thoseskilled in the art without departing from the spirit of the invention orthe scope of the claims.

What is claimed is:

1. In a device for producing aluminum or magnesium alloy castings of thetype having passageways formed therein, the combination with a patternof the article to be cast the dimensions of which exceed those of thearticle by the normal shrinkage allowances, of a conventional rnoldhaving a rnold cavity therein formed by said pattern, a core Within themold cavity for forming the passageways within the cast article, saidcore comprising an assembly of tubular elements of borosilicate glassand said core having a position within the mold cavity for the properlocation of the passageways, the dimensions Afor the size, shape andconguration of the core and the dimensions for the proper positioning ofthe core within the mold comprising the actual dimensions for theparticular article to be cast expanded by the same shrinkage allowancesas employed for the pattern.

2. In a device for producing aluminum or magnesium castings of the typehaving passageways therein, in combination, a conventional mold having amold cavity therein, and said mold having openings leading to the moldcavity providing a pouring gate and a riser respectively, a core ofborosilicate glass positioned within the mold cavity, said glass corehaving a size, shape and configuration corresponding to those of thedesired passageways and said core having a position within the moldcavity for the proper location of ythe passageways, the dimensions ofthe core and the dimensions for the proper positioning of the corewithin the mold comprising the actual dimensions for the particulararticle to be cast corrected only to compensate for the naturalcontraction of the casting, the said pouring gate and riser openingsbeing located a predetermined distance from the glass core to produce acasting to specied quality requirements.

3. A method of producing a cast metallic article characterized by havingintricate and complex passageways therein, the steps which includepreparing a mold by using a pattern of the article to be cast, thedimensions of which exceed those of the article by the normal shrinkageallowances, shaping a tube of borosilicate glass to form a core havingthe size, shape and congurations as desired for the passageways,positioning said core within the mold in the proper location as requiredfor the passageways, the dimensions for the size, shape andconfiguration of the core and the dimensions for the proper positioningof the core within the mold comprising the actual dimensions for theparticular article to be cast expanded by the same shrinkage allowancesas employed for the pattern, pouring molten metal in the mold andpermitting the metal to solidify, said metal being selected from thegroup consisting of aluminum and magnesium, removing the casting fromthe mold, and inally removing the glass core from the casting by flowinga chemical reagent through the same capable of corroding the glass corebut which is unreactive to the metal of the casting.

References Cited in the ile of this patent UNITED STATES PATENTS2,205,327 Williams June 18, 1940 l2,504,879 Brazil Dec. 15, 19422,362,875 Zahn Nov. 14, 1944 2,373,405 LOWit Apr. 10, 1945 2,494,403 NeSet al. Ian. l0, 1950 2,679,669 Kempa .Tune 1, 1954 OTHER REFERENCES IronAge, April 12, 1951, pages 107 to 109.

1. IN A DEVICE FOR PRODUCING ALUMINUM OR MAGNESIUM ALLOY CASTING OF THETYPE HAVING PASSAGEWAY FORMED THEREIN, THE COMBINATION WITH A PATTERN OFTHE ARTICLE TO BE CAST THE DIMENSIONS OF WHICH EXCEED THOSE OF THEARTICLE BY THE NORMAL SHRINKAGE ALLOWANCES, OF A CONVENTIONAL MOLDHAVING A MOLD CAVITY THEREIN FORMED BY SAID PATTERN, A CORE WITHIN THEMOLD CAVITY FOR FORMING THE PASSAGEWAY WITHIN THE CAST ARTICLE, SAIDCORE COMPRISING AN ESSEMBLY OF TUBULAR ELEMENTS OF BOROSILICATE GLASSAND SAID CORE HAVING A POSITION WITHIN THE MOLD CAVITY FOR THE PROPERLOCATION OF THE PASSAGEWAYS, THE DIMENSIONS FOR THE SIZE, SHAPE ANDCONFIGURATION OF THE CORE AND THE DIMENSIONS FOR THE PROPER POSITIONINGOF THE CORE WITHIN MOLD COMPRISING THE ACTURAL DIMENSIONS FOR THEPARTICULAR ARTICLE TO BE CAST EXPANDED BY THE SAME SHRINKAGE ALLOWANCESAS EMPLOYED FOR THE PATTERN.